Retroverted flow muffler



2 Sheets-Sheet l B. B. CARY ET AL RETROVERTED FLOW MUFFLER w m Y Wm A mw an? 5 fi MOM MN 0v. Em P. V? M m m J! M \N M \N 0% um m, m m t I u ulltl-llul I L. 8 "H T July 30, 1957 Filed Nov. 29, 1952 y 1957 a. B.CARY EI'AL 2,800,973

RETROVERTED FLOW MUFFLER Filed Nov. 29, 1952 2 Sheets-Sheet? INVENTORS5550mm 8. GARY LLOYD E. MULLER ATTORNEY RETROVERTED FLDW MUFFLER BeecherB. Cary, Rocky River, Ohio, and Lloyd E. Muller, Flint, MiclL; saidMuller assignor to General Motors Corporation, Detroit, Mich, acorporation of Delaware 7 I Application November 29, 1952, Serial No.323,180

4 Claims. (Cl. 181--57) This invention relates to sound attenuationapparatus and more particularly to mufilers for the exhaust gases ofinternal combustion engines.

It is a primary consideration in the construction of mufflers forautomotive vehicles to reduce to a minimum the power loss incident tothe sound attenuation of the exhaustgases prior to discharge to theatmosphere.

- Accordingly it is an object of this invention to provide a mufflerwhich dissipates a minimum amount of power and yet provides a maximumeflectiveness of sound atten-nation and to accomplish this objectwithout imposing limitations upon the external structural design or thetype of internal sound attenuation structure employed.

It is a particular object to provide a mufller of the re troverted gasflow type in which the energy loss incident to the reversal of thedirection of flow is minimized.

A further object is to provide a muifler in which the gasvelocity isconverted into static pressure which aids in the discharge of theexhaust gases through the remainder ofthe system.

C A further object is to provide a muffler in which the velocity of theexhaust gas is reduced smoothly without turbulence.

These and other objects will appear more fully hereinafter. Thev mannerof accomplishment is set forth in the description which follows togetherwith the accom panyin'g drawings in which:

Figure 1 is'aplan view of a muffler embodying the invention in which aportion of the outer casing is cut away to reveal the internalstructure.

' 'Figure 2 is a foreshortened sectional view of the mufller showing inplan the internal structure.

Figure3 is a sectional view taken transversely to the longitudinal axisof the device as indicated by the arrows 3--3 on Figure 2.

Figure 4 is a sectional view similarly taken at arrows 4-4 as indicatedon Figure 2.

Figure 5 is a cutaway sectional view showing a detail of construction ofthe outer casing and end header.

According to the present invention, the inlet passage of the retrovertedflow type of muffler is provided with a gradually increasing crosssectional area in the direction of gas flow. This construction permitsthe reduction' of exhaust gas velocity without turbulence and, as aresult of the decreased velocity, less kinetic energy is lost inreversing the gas flow. In addition the velocity head is converted tostatic head within the outer casing, and this static head is availableto force the gas through the rest of the exhaust system.

. Referring now to the drawings and particularly to Figtires 1 and 2 themufiler structure includes an outer casing 1 ..which may be of themultiple layer type as illustrated and formedin oval or ellipticallyshaped cross section. Such external configuration requires a minimum ofclearance and yet has desirable structural properties. The casing 1 isprovided .at the inlet end with an end header 2.

2,800,973 Patented July 3O, 1957:

2 The header 2 is secured to the casing 1 by any suitable means; forexample, by crimping a peripheral double walled flange of the end headerover an extension of the inner layer of easing 1 which is doubled uponitself. This detail of construction is illustrated in Figure 5.

The housing structure thus far described encloses the attenuating systemwhich embodies the present invention. The end header 2 is provided witha suitable opening offset from the central longitudinal axis of thecasing for the reception of an inlet tube 3. The inner end of the inlettube 3 is flared to receive in close supporting engagement,'as bytelescoping, the inlet conduit or casing 4 at its outer end 5. The inletconduit 4 extends asubstantial distance into the casing 1 and isreceived in supporting engagement adjacent its discharge end 6 by aflared edge 7' of an opening 7 in header 8. Intermediate its ends theinlet conduit 4 passes through an opening 9 in header 10 and is receivedthereby in close supporting relation by a flange 9 surrounding theopening, the openings in headers 8 and 10 being in alignment.

The inlet conduit 4 is tapered throughout its length to provide a crosssectional area which gradually increases from its outer end 5 to itsdischarge end 6. Intermediate the headers 8 and 10 is provided a thirdheader 11 through which the inlet conduit 4 passes with a clearancebetween it and the flared edge 12' surrounding the opening 12. Aplurality of perforations or louvers 13 are provided in the wall ofconduit 4 between the headers 10 and 11, and between the headers 8 and11.

Referring now to Figure 3 it will be seen that the header 10 having theaxial flange 9 is of elliptical shape. It is fitted transversely inclose engagement with the interior of the casing 1. The opening 9 isdisposed on the major axis of, but offset above the center of theheader. A similar circular opening 14 defined by axial flange 14' islikewise disposed on the major axis with its center positioned below theelliptical center. A pair of somewhat triangularly shaped openings 15surrounded by flanges 15' are provided, one on each side of the majoraxis. Be low the opening 14 is another opening 16 of suitable shape andof substantial area defined by flange 16.

In Figure 4 the structure of the header 8 is illustrated to be-similarto header 10 and has the circular opening 7 disposed above-center andprovided with the adjacent pair of openings 17 defined by flanges 17. Anenlarged opening 18 surrounded by flanged edge 18' of ovoid shape isdisposed in the lower portion of the elliptical header. The intermediateheader 11 is similar to header 8 in that it has an upper circularopening 12 described by the flange 12' and a lower enlarged opening 26defined by flanged edge 26.

Referring again to Figure 2, it will be seen that the exterior of flange14 around opening 14 in the header 10 receives the bell mouth end 19 ofoutlet conduit 20 in close supporting engagement. The conduit 20 extendsfrom header 10 to an end header 21, and is disposed in lateraljuxtaposition to conduit 4 to provide overlap of a substantial portionof the lengths of conduits 4 and 20 at the inlet end of easing 1. Theend header 21 may be of the same construction as end header 2 and may besimilarly secured to casing 1. The opening 22 in header 21 defined byflange 22' is in axial alignment with the opening 14 in the header 10.An outlet tube 23 having a bell mouth is received within flange 22 andsuitably secured as by flaring the edge of the bell mouth. The

discharge end 24 of conduit 20 is mounted in the bell:

mouth of outlet tube 23.

An outer tubular member 25 is mounted in coaxial 3 to a point adjacentheader 8. The conduit 20 is surrounded by axially disposed baffies 27,28, 29 and 30. The baffles 27 and 28 define a resonating chamber 31between tubes 20 and 25. Similarly, baffies 28 and 29 define a chamber32, and baffles 29 and 30 define a chamber 33. The interior of conduit20 communicates with chamber 31 through a plurality of perforations orlouvers 34. Likewise conduit 29 communicates with chamber 32 throughperforations 35 and with chamber 33 through perforations 36.

Intermediate the header 8 and the discharge end header 21 is positioneda transverse bafile 37 which is provided with an opening 38 surroundedby flange 38' to receive conduit 20 and suitably positioned to define anexpansion chamber 69 generally included between baflle 37 and end header2. A similar basfiie 40 is disposed between baffle 37 and the end header21 and defines resonating chambers 41 and 42. The interior of theconduit communicates with chamber 41 through a plurality of perforations43 and with chamber -42 through perforations 43'.

Viewed in its entirety as in Figures 1 and 2, it will now be apparentthat the inlet conduit 4 discharges into expansion chamber 39. Outletconduit 20 communicates with the expansion chamber 39 and with a seriesof resonating chambers 51, 3 2 and 33 suitably proportioned for thehigher range of frequencies of acoustic energy, and 41 and 42 designedfor a lower frequency range. Outlet conduit 2!) may communicate with theatmosphere either directly or through a tail pipe 43.

In the acoustic train each resonating chamber is adapted to damp out apredetermined frequency or frequency band of the acoustic energyaccompanying the exhaust gas discharge. The tuning to the desired rangeis accomplished by suitable dimensioning and propontioning of theparticular resonant chamber. The principle of operation of such anacoustic train is well understood in the art and the design may bevaried within wide limits or equivalent acoustic energy damping devicesmay be substituted. in one embodiment of the invention the componentparts were dimensioned as follows:

lnches Casing length 35 Elliptical cross section, major axis 9 AElliptical cross sect-ion, minor axis 5 Tapered inlet conduit length 20%Tapered inlet conduit outer end diameter 2 /2 Tapered inlet conduitinner end diameter 3 Outlet conduit length 31% Coaxial tube, diameter 3/2 Chamber 31, length 4 /2 Outlet conduit, diameter 2 /2 Chamber 32,length 5 Chamber 33, length 4% Chamber 41, length 4% Chamber 42, length3% It is to be understood that these dimensions are given for thepurpose of illustration only and are not to be construed as alimitation.

In operation the exhaust gases from the engine are fed to inlet tube 3from an exhaust pipe '44, the flow being represented by arrows 45. Thegases enter tapered inlet conduit 4 and since the gas velocity will beinversely proportional to the cross sectional area, neglecting leakage,the gas velocity is gradually reduced as the tlow progresses through theconduit 4. The gradual taper prevents turbulence and perm-its smoothflow. The portion of the flow 46 which emerges from the conduit 4 at end6 must reverse its flow direction in order to reach the mouth 19 of theoutlet conduit 20 .as indicated by the flow path 47. This reversal offlow direction dissipates kinetic energy of the moving gas, but sincethe flow velocity has been reduced, less energy is lost in making thereversal than would otherwise be the case.

A portion of the incoming gas passes through perforations 13 in the wallof conduit 4 as indicated by arrows 48. Since the velocity head of thegas in conduit 4 is converted into static head as the flow proceeds,this static head forces an increased flow through the perforations 1-3and thus reduces the quantity of gas required to make a reversal beyondthe inner end of conduit 4. The static head developed from the velocitychange is also available to force the gas through the remainder of theacoustic train.

The advantages achieved by the instant invention will be readilyappreciated by those skilled in the art. increased muffier efiiciency isrealized by reducing the energy loss without impairing the effectivenessof sound attenuation. Although the exemplary embodiment includes anelliptical casing and a particular attenuating system beyond the inletconduit, it will be recognized that the invention may be embodied inother and conventional mufiler structures. Many modifications andequivalents will occur to those skilled in the art and the illustrativeembodiment is in no sense to be construed as a limitation. For adefinition of the invention reference is to be had to the appendedclaims.

We claim:

1. In a sound attenuating apparatus of the retroverted flow typeincluding a mufller housing having first and second end members meanswithin said housing defining an expansion chamber, an inlet conduitwhich receives a gas flow at one end adjacent said first member andextends longitudinally into said housing terminating in an axialdischarge opening in said expansion chamber, an outlet conduit having anintake mouth which receives said gas flow and disposed in said expansionchamber, said outlet conduit being disposed with its intake mouthlongitudinally spaced from said discharge end and in spaced lateraljuxtaposition to said inlet conduit and extending through said secondmember, means for sup porting said conduits within said housing, saidinlet conduit having a perforate wall defining lateral dischargeopenings distributed substantially throughout its length within theexpansion chamber, said inlet conduit also having a cross sectional areawhich gradually and continuously increases in the direction of gas flow,and sound attenuation structure within said housing through which saidgas flow passes at a reduced flow velocity by virtue of said increase incross sectional area from said discharge end and said perforate wall tosaid intake mouth.

2. A muffler comprising a flattened elongated housing having a gas flowinlet at one end and a gas fiow outlet at the other, a plurality ofspaced supports in said housing, a perforated inlet conduit mounted incertain of said supports and laterally disposed in said housing, saidinlet conduit terminating in an axial discharge mouth and having agradually and continuously increasing cross section in the direction ofgas flow into said housing whereby said gas flow undergoes a change to areduced velocity and to an increased pressure, a perforated outletconduit mounted in certain of said supports laterally of said inletconduit and extending beyond the inner end of said inlet conduit toprovide a substantial overlap between said conduits requiring a reversalof said gas flow at said reduced velocity, and sound attenuatingchambers in said housing, said perforated conduits for conducting saidgas flow at said increased pressure into the said chambers in suchmanner as to absorb undesired frequency components of the soundaccompanying the gas flowing through said housing.

3. In a mufiler for the internal combustion engine exhaust gases of anautomotive vehicle, an elongated casing closed by an inlet end headerand an outlet end header, a plurality of intermediate headers in saidcasing defining an expansion chamber and sound attenuation chambers, anoutlet conduit supported by certain of said headers extending into saidcasing through said outlet end'header and terminating in an intake mouthin said expansion chamber adjacent said inlet end header,

an inlet conduit supported in certain of said headers extending intosaid casing through said inlet end header and terminating axially in afirst discharge opening in said expansion chamber beyond said intakemonth, said inlet conduit having a perforate wall within said expansionchamber and providing a second discharge opening, means supplying saidgases to said inlet conduit, said expansion chamber constituting a gasflow connection between said first and second discharge openings andsaid intake mouth requiring a reversal of flow direction, said inletconduit defining a passage having a gradually and continuouslyincreasing cross sectional area in the direction of gas flow eflectiveto reduce the flow velocity without turbulence as the flow proceedsthrough said passage, said reduced velocity and the incident increase instatic pressure being effective to cause increased flow through saidsecond discharge opening and less kinetic energy loss incident to theflow direction reversal.

4. In a muffier for the internal combustion engine exhaust gases of anautomotive vehicle, an oval casing closed by an inlet end header and anoutlet end header, a first transverse bafile disposed in said casingdefining an expansion chamber between said bafile and said inlet endheader, a second transverse bafiie disposed between said first bame andsaid outlet end header defining a first set of resonating chambers, aplurality of intermediate headers in said expansion chamber, an outletconduit extending into said expansion chamber through said outlet endheader and said baflies to an intermediate header adjacent said inletend header, a tubular member in external coaxial relation with saidoutlet conduit defining an axially extending annular chamber, aplurality of annular bafiles disposed therein to define a second set ofresonating chambers, the portions of said outlet conduit extendingthrough said first and second sets of resonating chambers comprising aperforate wall, an inlet conduit extending into said expansion chamberthrough-said inlet end header and said intermediate headers andterminating in a-first discharge opening adjacent the said first bafile,said inlet conduit having a perforate wall providing second dischargeopening and a gradually increasing cross sectional area in the directionof gas flow and disposed in lateral juxtaposition to said outlet conduitthereby requiring a reversal of flow direction of the portion of gasflow leaving the first discharge opening, said gradually increasing areaof said inlet conduit effecting a decrease of flow velocity as the flowproceeds in the inlet conduit, whereby the resulting static pressureincrease is effective to force additional fiow through said seconddischarge opening reducing the quantity of gas leaving the firstdischarge opening required to undergo a flow reversal, and whereby theresulting decreased velocity decreases the energy loss incident to theflow reversal.

References Cited in the file of this patent UNITED STATES PATENTS1,305,347 Fekete June 3, 1919 2,036,138 Haas Mar. 31, 1936 2,125,449Kingsley Aug. 2, 1938 2,337,300 Noblitt et a1. Dec. 21, 1943 2,357,791Powers Sept. 5, 1944 2,614,647 Bryant Oct. 21, 1952 2,652,128 Cary Sept.15, 1953 FOREIGN PATENTS 3,354 Great Britain Feb. 12, 1906 781,087France Feb. 18, 1935

